No, I simply made the cap location modification to an existing circuit whose
Source resistors reflected the desire for some 2nd harmonic by different
degeneration top vs bottom.
Ok. I think I understand what you are saying.
You took the existing curcuit diagram from the F6 article and changed the cap wiring in the circuit but forgot to change source resistors to both 0.47Ohms?
He means the source resistors are different, he just changed the cap lead location.
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Yes but there is no reason to keep different source resistors.
It's definitely confused a lot of people.
I'm guessing he just forgot to change the values to the same value.
I'm not Nelson (obviously haha)
My understanding is the circuit he released is a representation of the production Firstwatt F6 circuit. Nelson would have hand selected mosfets to get the sound he wanted rather than use degeneration.
In my opinion this is the preferred method but requires more work for the diyer.
This amp has had me dumb founded on many levels. I don't want to high light the other differences, I think people are confused enough already.
This is definitely my favourite amp circuit so far.
They serve absolutely no purpose in that circuit.
I'm sure even our Legend Guru Papa forgets/overlooks/makes mistakes occasionally.
I forget stuff all the time, even forget my boss's name and I'm only 42. Hahahaha
Nelson said that different source resistors still help the DC degeneration.(referring to the non degenration schematic)
Nelson himself agrees with what I have said, at least he has not corrected the observations I have made.
My distortion analyzer doesn't lie (touch wood).
Nelson knows exactly what he is doing, I would also choose to do it the way he has chosen.
What Nelson just wrote implies to me he forgot to change the source resistor values. For your information the circuit is also not an exact clone of the Firstwatt F6.
Nelson has a history of making mistakes in circuits (eg F5 article), he is human like the rest of us, nothing to be ashamed about.
I hold Papa in the highest esteem for many reasons.
My distortion analyzer doesn't lie (touch wood).
Nelson knows exactly what he is doing, I would also choose to do it the way he has chosen.
What Nelson just wrote implies to me he forgot to change the source resistor values. For your information the circuit is also not an exact clone of the Firstwatt F6.
Nelson has a history of making mistakes in circuits (eg F5 article), he is human like the rest of us, nothing to be ashamed about.
I hold Papa in the highest esteem for many reasons.
That's basically what I suggested was their purpose just a few posts back and Nelson said that was incorrect.
If you read what he said 10 times carefully, to me he is simply stating he took the original circuit and moved the cap position. The different source values are just the remnants of the previous circuit.
I'm not interested in proving anything. I've flogged this horse both in simulation and on my distortion analyzer, people are free to believe what they want. There is definitely more I could do, but my time is limited.
Nelson will correct my observations if they are wrong.
This might be right, but instead of speculating I would like to hear it from Papa.
boyz ......... you really made a mess with simple non-issue
you need both DC and AC degeneration ...... first one serving for bias/offset stability , second one serving as THD spectra tool
what can be possible object for question addressed to Pa is to ,once for ever, he reply with definitive values of upper and lover source resistor ........ separately for Semisouth and IRFP iteration
I believe there are already published exact schematic for both (including that one with Generg's Zen Amount Pot solution ) ...... but I'm lazy to search for them
you need both DC and AC degeneration ...... first one serving for bias/offset stability , second one serving as THD spectra tool
what can be possible object for question addressed to Pa is to ,once for ever, he reply with definitive values of upper and lover source resistor ........ separately for Semisouth and IRFP iteration
I believe there are already published exact schematic for both (including that one with Generg's Zen Amount Pot solution
) ...... but I'm lazy to search for themAnother explanation for both AC and DC degeneration:
- DC degeneration is needed for DC stability, in particular to reduce the increase of drain current as the FET temperature rises.
- AC degeneration modifies the transconductance of the FETs, allowing control of the 2nd harmonic magnitude and phase.
Just move the cap leads.
If you don't want to do that, and not setup to measure transconductance then another option is to order one IRFP250 and one IRFP240. That will give you plenty of second harmonic.
I am sure your equipment in your lab is far superior to what Nelson uses at Firstwatt and of course there is nothing in your observations in simulation and with your superior equipment and testing that you have not thought of or not made a mistake in with your superior electronic background. Only someone with your equipment and knowledge would even think of telling the forum Nelson made a mistake. I noticed he changed the positions of the value of the resistors months ago and asked why he did so and Nelson did not think if worthy of commenting on. No mistake has been made. It has been designed exactly for the sound Nelson was looking for. You say the F6 commercial version is different from the one given to diyer's. I did not know you had privileged information none of us have. For quality control I could see a circuit somewhat different to provide a consistent product but your statement is the first I have heard of this. From what I have read a lot of testing and listening was done with the 2 versions of F6 before deciding that the Mosfet version sounded the best. The changes were made because of the different transistors.
I did not think Nelson would think it necessary to comment on your telling the forum you think he just made a mistake or forgotten to make changes and that you are correct. It would be a waste of his valuable time. I am sure you will provide more rhetoric and confuse more beginning builders and the more knowledgeable builders will just ignore you as I probably should.
Experimentation is good and trying different ways sometimes leads to changes that others find better sounding but it would be a far stretch to accuse a Master designer considered the best in his field as making a mistake. As I have stated an apology would be the gentlemanly thing to do and a statement like "to me the circuit changes I suggest has more of an effect with the 2nd harmonic" if that is what you truly believe instead of boldly stating that in your opinion Nelson just forgot something.
Zen Mod stated in fewer words what is really happening with the resistors. You state that your time is very limited, I am guessing your field is designing and building amplifiers as Nelson's is. His lifetime occupation has been and is designing amplifiers and not a sideline from another job.
I should just have ignored your comments as others have but your statement that Nelson must have forgotten something just rubbed me the wrong way.
As you have said the members can choose what to believe.
You seem irritated. I have no idea why.
Zen Mod and I are in complete agreement.
Here is a video showing source 0.56/0.47 to 0.56/0.235 on the fly on the DIYAUDIO PCB circuit (which is different from the F6 article)
Meter is setup to just measure 2nd harmonic. Changing source resistor from 0.47 to 0.235 ( 2 x 0.47 Ohms in Parallel) has no significant effect on the second harmonic.
https://www.youtube.com/watch?v=7nJWP_DUaBY
If you read the F6 article a few times, there is nothing I have said that disagrees with Nelson.
Zen Mod and I are in complete agreement.
Here is a video showing source 0.56/0.47 to 0.56/0.235 on the fly on the DIYAUDIO PCB circuit (which is different from the F6 article)
Meter is setup to just measure 2nd harmonic. Changing source resistor from 0.47 to 0.235 ( 2 x 0.47 Ohms in Parallel) has no significant effect on the second harmonic.
https://www.youtube.com/watch?v=7nJWP_DUaBY
If you read the F6 article a few times, there is nothing I have said that disagrees with Nelson.
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